Ivory is going to run you around $300. on up. You can buy ivory grips all day long with no hassle on Gunbroker and ebay. Stag goes for around $100. on up. A nice set of wood grips may run you $100. or thereabouts. It just depends on your budget and your taste.
Personally, I lean towards Sambar Stag. With the right coloration and bark, it can be just beautiful on a six shooter.
If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen. ― Samuel Adams